1. Field of the Invention
The field of art to which this invention pertains is catalytic composites, methods of their manufacture, and the use thereof. More specifically, the claimed invention relates to a catalytic composite comprising a calcined mixture of a zeolitic crystalline aluminosilicate, a refractory inorganic oxide, and an ammonium salt, a method of preparing the catalytic composite by calcining a zeolite of the mordenite crystal structure in admixture with a refractory inorganic oxide and an ammonium salt, and a method of using the aforesaid catalytic composite in treating sour petroleum distillates.
2. Description of the Prior Art
Crystalline aluminosilicates, or zeolites, of which mordenite is one example, are well known in the art and have found extensive application as hydrocarbon conversion catalysts or as a component thereof. Such materials are of ordered crystalline structure often visualized as a three-dimensional network of fundamental structural units consisting of silicon-centered SiO.sub.4 and aluminum-centered A1O.sub.4 tetrahedra, the tetrahedra being interconnected by a mutual sharing of apical oxygen atoms and arranged to form cages or cavities in open communication through smaller intracrystalline channels of pore openings whose narrowest cross section has essentially a uniform diameter characteristic of each crystalline aluminosilicate variety. To effect a chemical balance, each A1O.sub.4 tetrahedra has a cation associated therewith--usually a sodium or other exchangeable cation. The aforementioned cages or cavities are occupied by water molecules and by the last mentioned cations, both of which exhibit considerable freedom of movement permitting ion-exchange and reversable dehydration.
The crystalline aluminosilicates, or zeolites, employed in the manufacture of the catalytic composite of this invention, are of the mordenite crystal structure, highly siliceous in nature and generally characterized by a silica-alumina mole ratio of from about 6 to about 12 as found in nature. The mordenite crystal structure comprises four- and five-membered rings of the SiO.sub.4 and AlO.sub.4 tetrahedra so arranged that the crystal lattice comprises pores and channels running parallel along the crystal axis to give a tubular configuration. This structure is unique among the crystalline aluminosilicates since the channels of tubes do not intersect, and access to the cages or cavities is in only one direction. For this reason, the mordenite structure is frequently referred to as two-dimensional. This is in contrast to other well-known crystalline aluminosilicates, for example faujasite, in which the cavities can be entered from three directions. Mordenite, clinoptilolite, or mordenite which has been synthesized or acid extracted, caustic extracted or otherwise treated to increase the silica-alumina mole ratio to about 20:1 or more while maintaining the mordenite crystal structure, may be used in the manufacture of the catalytic composite of this invention.
Crystalline aluminosilicate having a mordenite crystal structure have heretofore been utilized composited with a refractory inorganic oxide, typically alumina, as a hydrocarbon conversion catalyst, and are particularly useful with respect to the transalkylation of alkylaromatic hydrocarbons. It is an object of this invention to present a new and useful method of manufacture providing a novel catalytic composite of improved activity, especially useful in the treatment of sour petroleum distillates.
Catalysts manufactured simply by compositing a crystalline aluminosilicate having a mordenite crystalline structure with a refractory inorganic oxide typically have been of relatively low activity. The prior art reveals that methods of manufacturing catalysts of improved activity have required steps in addition to a simple composite step, often involving the use of hazardous chemicals.
The prior art discloses that in preparing a catalytic composite comprising a crystalline aluminosilicate having a mordenite crystalline structure containing less than about 5 wt. % sodium as Na.sub.2 O and a refractory inorganic oxide, activity of the catalytic composite may be increased by the addition during compositing of a peptizing agent such as nitric acid. The prior art also discloses that a catalytic composite of improved activity can be prepared by subjecting the crystalline aluminosilicate to an aqueous ammoniacal treatment at a pH of at least 9.5 prior to admixture with the refractory inorganic oxide and addition of the peptizing agent. U.S. Pat. No. 4,107,086. The prior art further discloses that another method of improving catalyst activity comprises the addition during compositing of a certain quantity of a metal salt convertible at calcination conditions to the refractory metal oxide composited with the crystalline aluminosilicate, and subjecting either the crystalline aluminosilicate prior to compositing or the resulting composite to an aqueous ammoniacal treatment at a pH of at least 9.5. U.S. Pat. No. 4,039,479.
What has been needed, but not shown by the foregoing prior art, is a catalytic composite with activity comparable to or superior to that of the prior art which can be manufactured conveniently and less expensively in fewer steps. Such a catalytic composite has been accomplished in the present invention. Whereas the prior art requires that a strong acid peptizing agent by used in the manufacture of active catalytic composites of mordenite and a refractory inorganic oxide, the catalytic composite of this invention is of superior activity and yet can be prepared without a peptizing agent, using instead a neutral ammonium salt. Thus the use of hazardous peptizing agent chemicals can be avoided. The ammonium salt admixed in the preparation of the catalytic composite of this invention can be in any form, including powder or aqueous solution. Thus, there exits inherently greater flexibility in the manufacture of the catalytic composite of this invention as opposed to prior art catalytic composites which require liquid solutions of peptizing agents. Further, the preparation of the catalytic composite of this invention requires fewer steps than the preparation of catalytic composites disclosed in the foregoing references, since no aqueous ammoniacal treatment of the mordenite or the resulting catalytic composite is required.